Preparation of aromatic carboxylic acids

ABSTRACT

Disclosed is a process for the production of aromatic carboxylic acids by the carbonylation of aromatic bromides in the presence of a nickel catalyst, a Bronsted base and an iodide promoter.

This is a continuation of application Ser. No. 026,917, filed Mar. 17, 1987, now abandoned.

This invention relates to a process for the preparation of aromatic carboxylic acids by the reaction of aromatic bromides with carbon monoxide in the presence of a nickel catalyst, a Bronsted base, and an iodide promoter.

The carbonylation of aromatic halides in the presence of nickel to obtain aromatic carboxylic acids is well known in the art. Nakayama and Mizoroki (Bull. Chem. Soc. Japan 42,1124 (1969)) disclose the nickel-catalyzed carbonylation of aromatic bromides in the presence of potassium acetate and water at 250° C. and 2844 psig to produce the corresponding carboxylic acid. In order to achieve an acceptable rate of reaction, it is common in the art to conduct the carbonylation of aromatic bromides and chlorides at extremely high temperatures and pressures.

It would therefore be an advance in the state of the art to provide a simple process by which aromatic bromides could be carbonylated to their respective aromatic carboxylic acids in high yields under milder reaction conditions.

In accordance with the present invention, it has now been found that aromatic bromides can be carbonylated to the desired aromatic carboxylic acids under mild reaction conditions by the use of the combination of a nickel catalyst, a Bronsted base and an iodide promoter.

The aromatic bromides which may be used in our process may be monobromo or polybromo e.g. di-, tri-and tetra-bromo aromatic compounds. The aromatic nucleus or moiety can contain from 6 to 18 carbon atoms, preferably 6 to 10 carbon atoms and may be carbocyclic aromatic such as benzene, biphenyl, terphenyl, naphthalene, anthracene, etc., or heterocyclic aromatic such as pyridine, thiophene, pyrrole, indole, etc. In addition to one or more bromine atoms, the aromatic moiety may be substituted by various substituents inert under the conditions employed in our process. Examples of such substituents include alkyl of up to about 12 carbon atoms such as methyl, ethyl, isobutyl, hexyl, 2-ethylhexyl, nonyl, decyl, dodecyl, etc.; cycloalkyl of about 5 to 12 carbon atoms such as cyclopentyl, cyclohexyl, 4-butylcyclohexyl, etc.; hydroxy; alkoxy of up to about 12 carbon atoms such as methoxy, ethoxy, propoxy, butoxy, octyloxy, etc.; halogen such as chloro and bromo; alkoxycarbonyl of from 2 to about 8 carbon atoms such as methoxycarbonyl, ethoxycarbonyl, butoxycarbonyl, hexyloxycarbonyl, etc.; carboxyl; cyano; alkenyl of about 2 to 12 carbon atoms such as vinyl, allyl, etc.; formyl; alkanoyl of about 2 to 8 carbon atoms such as acetyl, propionyl, butyryl, hexanoyl, etc.; alkanoylamido of about 2 to 8 carbon atoms such as acetamido, butylamido, etc.; aroylamino such as benzamido; and alkylsulfonamide such as methanesulfonamide, hexanesulfonamido, etc.

Specific examples of the aromatic bromide reactants include bromobenzene, 1,3- and 1,4-dibromobenzene, 1,3,5-tribromobenzene, 4-bromotoluene, 4-bromophenol, 4-bromoanisole, 4-bromoacetophenone, 4,4'-dibromobiphenyl, 4-chlorobromobenzene, and 2,6- and 2,7-dibromonaphthalene. Our process is particularly useful for the preparation of benzenedicarboxylic and naphthalenedicarboxylic acids and thus the preferred reactants are dibromobenzenes, especially 1,3- and 1,4-dibromobenzene, and dibromonaphthalenes, especially 2,6- and 2,7-dibromonaphthalene.

The aromatic bromide reactants are known compounds and/or can be prepared according to published procedures. For example, T. Hudlicky et al The Chemistry of Halides, Pseudohalides and Azides, Supplement D, Part 2, 1102-1136, the disclosure of which is incorporated herein by reference in its entirety, discloses a number of such processes.

In the process of this invention, the aromatic bromide is carbonylated in a carboxylic acid reaction medium created by use of a carboxylic acid, such as acetic acid, butyric acid, propionic acid, benzoic acid, and the like or mixtures thereof, with acetic acid being the most preferred. Also, the carbonylation reaction can tolerate substantial quantities of water.

The nickel catalyst can be provided to the reaction medium as either nickel metal or as any of a number of nickel salts or complexes. Illustrative sources of nickel are nickel acetate, nickel chloride, nickel bromide, nickel iodide, nickel carbonate, nickel hydroxide, nickel oxide, nickel acetylacetonate, nickel tetracarbonyl and its phosphine and halogen substituted analogs. The amount of nickel is not significant as long as enough is present to catalyze the reaction. Preferably, the catalyst is present in a concentration of 10 to 0.001 mole percent, preferably 2.5 to 0.1 mole percent, based on the moles of aromatic iodide reactant. Therefore, the total reaction medium has a catalyst concentration of about 10,000 ppm to 1 ppm with preferred catalyst concentrations of 1,500 to 100 ppm.

A Bronsted base is also added to the carboxylic acid reaction medium to maintain and enhance the reaction rate of the carbonylation process. By the term "Bronsted base" we mean any substance that can act as a proton acceptor in the reaction medium. In particular, the Bronsted base can be an acetate, formate, hydroxide, carbonate or alkoxide of an alkali, alkaline earth transition or non-transition metal. The Bronsted base can be added in an amount of about 1 percent to about 15 weight percent, based on the amount of the carboxylic acid reaction medium, preferably about 2 to 10 weight percent. Examples of a Bronsted base are alkali metal carbonates, such as lithium carbonate, as well as alkali metal acetates such as lithium acetate, sodium acetate, potassium acetate and the like, preferably lithium acetate. Alkaline earth metal acetates, such as magnesium acetate, can also be used. Transition and nontransition metal acetates such as iron, manganese, zinc and tin acetates can also be used. Amines such as pyridines and trialkylamines, for example triethylamine or trimethylamine, can be used. Alkali metal acetates can be generated in situ by adding an alkali metal component, such as lithium carbonate, to the carboxylic acid reaction medium such as acetic acid, to form lithium acetate. Also alkyl acetates, such as methyl acetate, can be used when in the presence of an alkali or alkaline earth metal iodide. Alkyl acetates can also be generated in situ by adding an alkanol, such as methanol, to the reaction medium which reacts with the anhydride by-product to form the alkyl acetate.

An alkali or alkaline earth metal iodide which functions as an iodide promoter is also added to the carboxylic acid reaction medium to enhance the carbonylation rate of the carbonylation process. By the term "iodide promoter" we mean an alkali or alkaline earth metal iodide that is capable of providing a soluble form of iodide in the reaction as any number of salts or complexes. Illustrative examples are alkali metal iodides such as lithium iodide, sodium iodide, potassium iodide, rubidium iodide and alkaline earth iodides such as magnesium diiodide, calcium diiodide, strontium diiodide and barium diiodide. The iodide promoter can be added in an amount which results in catalytic activity. Specifically, the amount can be about 0.5 to 25 weight percent, based on the amount of the carboxylic acid reaction medium, preferably 5 to 15 weight percent.

The carbonylation reaction is conducted in the presence of carbon monoxide, which is employed in amounts such that the total reaction pressure is suitable for the formation of the aromatic carboxylic acid. The carbon monoxide employed may be essentially pure or it may contain other gases such as carbon dioxide, hydrogen, methane and other compounds produced by synthesis gas plants. Normally, the carbon monoxide will be at least 90, preferably at least 95, percent pure.

The process of the present invention can be conducted at temperatures and pressures suitable for formation of the aromatic carboxylic acid. The temperatures and pressures are interdependent and can vary considerably. Normally, the pressure will be at least 100 psig. While the process can be carried out at pressures as high as 10,000 psig, the cost of utilities and equipment required for such high pressure operation cannot normally be commercially justified. Thus, the pressure normally will be in the range of about 125 to 4000 psig, preferably about 300 to 1000 psig. A particularly preferred pressure is 750 to 1000 psig. While temperatures as low as 125° C. and higher than 225° C. may be used, our process normally is carried out between about 125° to 225° C. The preferred temperature range is 150° to 200° C.

The process of this invention is particularly useful for the preparation of aromatic dicarboxylic acids such as 1,3- and 1,4-benzenedicarboxylic and 2,6- and 2,7-naphthalenedicarboxylic acids. Such diacids may be used in the preparation of polyesters such as poly(ethylene terephthalate) and poly-(ethylene 2,6-naphthalenedicarboxylate).

The process of this invention can be carried out as a batch, semi-continuous or continuous operation. In the manufacture of aromatic dicarboxylic acids in the quantities required for use in the preparation of polyesters such as those mentioned above, the process described hereinabove will be carried out in a continuous manner. A typical continuous method of practicing our process comprises feeding into a mixed pressure vessel a liquid stream composed of 2,6-dibromonaphthalene in acetic acid, the nickel catalyst, the Bronsted base, the iodide promoter and a gaseous stream of carbon monoxide. The pressure vessel is equipped with a means for maintaining the desired temperature and pressure. The liquid mixture from the reactor column is centrifuged and 2,6-naphthalene dicarboxylic acid is separated from the solution which is recycled.

The iodide can be recovered from the reaction medium by several methods. For example, when the reaction medium is acetic acid and a stoichiometric amount of a metal acetate, such as lithium acetate, is present, acetic anhydride, lithium iodide and lithium bromide are formed as reaction by-products. Reactive distillation of the acetic anhydride from the lithium halide containing reaction mixture provides the acetyl halides and lithium acetate. If a metal acetate, such as lithium acetate, is not present then the acetyl halides are formed as the reaction by-product. The acetyl iodide can be separated and recovered by distillation. The recovered acetyl iodide can then be hydrolyzed with water to form acetic acid and hydrogen iodide which can be recovered or oxidized to recover the iodide present.

Another method for recovery of the iodide is to add oxygen to the reaction medium which readily oxidizes the iodide to elemental halide. The elemental iodide can be recovered by distillation, filtration or other suitable means. This method provides a good cost effective and efficient method for iodide recovery whereby the relatively expensive iodide can be recovered and recycled continuously.

Our invention is further illustrated by the following examples. In the procedures utilized in the examples the materials employed are loaded into a 330 ml autoclave constructed of Hastelloy B2 alloy which is designed to operate in a rocking mode. The autoclave is pressurized with 500 psig carbon monoxide gas pressure at room temperature and then the gas is vented and the autoclave is sealed. In these examples the autoclave is pressurized to 250 psig with carbon monoxide gas at ambient temperature and heated and rocked until reaction temperature was reached, at which time additional carbon monoxide gas is added to increase the autoclave internal pressure to the predetermined value. Reactor pressure is maintained by adding carbon monoxide at the same rate at which it is consumed by the reactants. The carbon monoxide used is essentially pure. When the predetermined reaction time is completed the autoclave is cooled by a stream of cold air to approximately 25° C. After the gas is vented from the autoclave the crude product is analyzed by gas chromatographic methods. The % conversion is the mole percent of bromo-group converted to carboxylic acid. The results of these runs are shown below.

    __________________________________________________________________________              Example No.                                                                    1         2         3        4       5       6                        __________________________________________________________________________     Bromoaromatic                                                                           1,4-dibromobenzene                                                                       1,4-dibromobenzene                                                                       2-bromo-6-methyl                                                                        bromobenzene                                                                           bromobenzene                                                                           bromobenzene             wt (g)   20        20        naphthanoate                                                                            40      40      40                                                    0.61                                              Nickel   Ni(OAc).sub.2.4H.sub.2 O                                                                 Ni(OAc).sub.2.4H.sub.2 O                                                                 NiI.sub.2                                                                               NiI.sub.2                                                                              NiI.sub.2                                                                              NiI.sub.2                Catalyst 1.7       1.7       2.0      2.14    2.14    2.14                     wt (g)                                                                         Bronsted Li.sub.2 CO.sub.3                                                                        Li.sub.2 CO.sub.3                                                                        Li.sub.2 CO.sub.3                                                                       Li.sub.2 CO.sub.3                                                                      Li.sub.2 CO.sub.3                                                                      Li.sub.2 CO.sub.3        Base     1.0       1.0       4.0      4.0     4.0     0.5                      wt (g)                                                                         Iodide   LiI       --        LiI      LiI     LiI     LiI                      Promoter 10        --        10.0     4.0     0.5     4.0                      wt (g)                                                                         Carbocyclic                                                                             acetic acid                                                                              acetic acid                                                                              acetic acid                                                                             acetic acid                                                                            acetic acid                                                                            acetic acid              Acid Reaction                                                                           105       105       105      156     155     155                      Medium                                                                         wt (g)                                                                         Time (Hr)                                                                               3         3         3        3       3       3                        Pressure 1000      1000      1000     750     750     750                      (psig)                                                                         Temp (°C.)                                                                       190       190       175      175     175     175                      % Conversion                                                                            16        0         100      16.1    2.5     8.8                      __________________________________________________________________________

While the invention has been described in detail with particular reference to preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 

We claim:
 1. A process for the production of aromatic carboxylic acids which comprises carbonylating aromatic bromides in the presence of a carboxylic acid, carbon monoxide, a catalytic amount of nickel, a Bronsted base and an alkali or alkaline earth metal iodide.
 2. The process of claim 1 wherein the aromatic bromides are selected from dibromonaphthalenes and dibromobenzenes.
 3. The process of claim 2 wherein the dibromonaphthalene is 2,6-dibromonaphthalene and the dibromobenzene is 1,4-dibromobenzene.
 4. The process of claim 1 wherein the temperature is in the range of about 125° to 225° C.
 5. The process of claim 4 wherein the temperature is in the range of about 150° to 200° C.
 6. The process of claim 1 wherein the pressure is in the range of 125 to 4,000 psig.
 7. The process of claim 6 wherein the pressure is in the range of 300 to 1,000 psig.
 8. The process of claim 1 wherein the alkali metal iodide is selected from the group consisting of lithium iodide, sodium iodide, potassium iodide and rubidium iodide.
 9. The process of claim 1 wherein the alkaline earth metal iodide is selected from the group consisting of magnesium diiodide, calcium diiodide, strontium diiodide and barium diiodide.
 10. The process of claim 1 wherein the Bronsted base is selected from the group consisting of alkali, alkaline earth and transition metal acetates, formates, hydroxides, carbonates and alkoxides.
 11. The process of claim 10 wherein the Bronsted base is an alkali metal carbonate.
 12. A process for the coproduction of aromatic dicarboxylic acids selected from benzene dicarboxylic acids and naphthalene dicarboxylic acids which comprises carbonylating a dibromobenzene or a dibromonaphthalene at a temperature of about 150 to 200 degrees centigrade and a pressure of about 300 to 1,000 psig in the presence of acetic acid, carbon monoxide, lithium carbonate, lithium iodide, and a catalytic amount of nickel acetate. 